1. Field of the Invention
The present invention relates to an optical recording medium. In particular, the present invention relates to a recordable optical recording medium that can densely record data as well as has high recording stability.
2. Description of the Related Art
With the advent of multimedia age comprehensively dealing with video signal including moving picture and stop picture, audio signal, and computer data information, package media including all kinds of discs like CD and DVD have been widely used. Recently, there have been active efforts to apply an optical recording medium to the recording media of mobile phone, digital camera, broadcasting, and movie.
The optical recording medium is divided into read-only memory (ROM) optical recording medium, recordable optical recording medium capable of recording information only once, and rewritable optical recording medium capable of writing, reading, and deleting information repeatedly.
The recordable optical recording medium can be applied for data backup or storage of broadcasting, movie, etc. As recording layer material of the recordable optical recording medium, organic material like dye or inorganic material may be used. Only, in case of using organic material as the recording layer material, a problem may be occurred in long term storage of data recorded in the optical recording medium.
As recording mechanisms of the recordable optical recording medium, a) a pit is generated when the recording layer material is burned, b) a pit is formed from expansion of the volume as the recording layer material is decomposed, c) a new phase is formed by solidifying after the recording layer is melted, or d) a new material (for example, silicide, germanium compound, or antimony compound) is formed by reaction on the contact surface with foreign material.
Also, multiple mechanisms may occur to generate the recording mark. In case the recording mark is generated by multiple mechanisms, if a laser beam is irradiated onto the optical recording medium, first material and second material in the recording layer may be mixed and changed to form different material from those of the recording layer.
In this case, data are recorded by optical property changed in the recording layer material, and the recorded data can be identified by change of reflectivity according to the changed optical property before and after recording.
In order for the multiple mechanisms to occur in the optical recording medium, the optical recording medium needs to have an internal structure to generate such mechanisms and a combination of the recording layer material suitable to the internal structure.
On the other hand, record medium for next generation requires very high recording density and transmittance velocity for data. The size of recording mark of the optical recording medium should be smaller than the present size to increase the recording density recorded in the optical recording medium. Thus, the laser wavelength irradiated onto the optical recording medium should be reduced to 450 nm or less, and the numerical aperture should be increased to 0.7 or more. Also, the data transmittance velocity should be much higher than the present one of between 30 Mbps and 35 Mbps.
In case of BD (BLU-RAY DISC) that is one of recording media for next generation, a recording layer material having characteristic of jitter acceptable within the ranges of recording linear velocity of between 5.28 m/s and 10.56 m/s and a laser power of between 3 mW and 7 mW at 405 nm wavelength should be included in the optical recording medium.
Particularly, the recordable optical recording medium having the above characteristic requires combination of the recording layer material in which, i) the contrast between recording mark and space in the optical recording medium should be high, ii) the recording sensibility should be high, iii) recorded mark should be stable, and iv) recording characteristics including noise and jitter of recording mark should be satisfied in BD system.
Also, in case the recording mark is made inside the optical recording medium by irradiated laser, combination of recording layer material is required to prevent the laser power needed for making recording mark from being too high.